This invention relates to a gas lock for hypodermic needles and more particularly to such a needle used in conjunction with a hypodermic syringe containing blood which is to be analyzed with regard to the gases dissolved therein.
As is well known in the field of medicine, it is frequently valuable, in diagnosing a patient's illness, to analyze the gases dissolved in the patient's blood and the equipment for analyzing such gases is universally available. A problem arises, however, in that the accuracy of the analysis is determined by an ability to analyze the blood as withdrawn from the patient with a minimal amount of the blood gases evolving from the solution and being lost, and with a minimum amount of contamination of the blood by the dissolution therein of gases from the surrounding atmosphere after the blood has been withdrawn. In this regard it is noted that, as a practical matter, a substantial period of time frequently elapses between the time the blood is withdrawn from the patient and the time it reaches a laboratory for analysis.
Medical personnel, recognizing the loss of accuracy caused both by contamination of the blood and by its "staleness", that is, gases originally dissolved in the blood have evolved out, have devised various means to minimize the lack of accuracy. For example, it has been proposed that the hypodermic syringe be inserted into a rubber stopper immediately after blood withdrawal, thereby sealing the single gas passage in the hypodermic unit (syringe and needle). In this regard, medical technicians frequently take the extraordinary measure of destroying expensive evacuated containers, commonly known as "vacutainers", merely to obtain the rubber stoppers from such containers. Theoretically, this should provide a satisfactory solution to the aforementioned problem. As a practical matter, however, it has not been satisfactory. This is due to the fact that the rubber stoppers frequently become dislodged from the hypodermic needles thereby permitting blood gas loss and permitting contamination of the blood. Further, the hypodermic needles are frequently drive completely through the rubber stoppers resulting in the open, puncturing, end of the needle not being within, and enveloped by, the rubber stopper. This last defect, of course, causes an additional problem in that the sharply pointed puncturing end of the hypodermic needle is exposed and can therefore injure medical personnel handling the hypodermic units. Finally, utilization of a rubber stopper only at the puncturing end of a hypodermic needle suffers from the additional defect that the slender hollow needle may easily be broken, thereby both permitting contamination or gas leakage and resulting in a sharply pointed instrument being exposed.